Cardiac autonomic imbalance has been suggested as a possible cause of sudden infant death. This imbalance has been reported to be greater in premature infants than in full-term neonates. At present, little is known of effects of commonly used sympathomimetic agonists, such as epinephrine, isoproterenol and antagonists such as propranolol on fetal cardiac rate and rhythm. The objective of the proposed research is to determine effects of autonomic mediators on cellular electrophysiologic characteristics of fetal and neonatal hearts. Using standard intracellular microelectrode recording techniques to study hearts obtained from fetuses of early, middle and late gestation, I plan to determine: 1) the ontogeny of celluclar electrophysiologic properties of the ventricular specialized conducting system, sinus node preparations and working myocardium and 2) the effects of cholinergic agonists and antagonists and of adrenergic agonists and antagonists on cellular electrophysiologic properties of the developing heart. The information obtained from the proposed research should be of value not only to our understanding of normal development of cellular electrophysiologic properties, but also to our understanding of disturbances in cardiac rate and rhythm which arise as a result of maternal administration of pharmacological agents which affect heart rate and rhythm in the fetus.